The present invention relates to a process for the production of (cyclo)aliphatic diisocyanates having isocyanate groups in the 1,2-position or the 1,3-position to one another.
Preparation of organic isocyanates by reacting amines with phosgene in the gas phase is known. (See, for example, Siefken, Justus Liebigs Ann. Chem. 562, 108 (1949)). However, such processes have, until now, been recommended only for the preparation of monoisocyanates (Ullmann, 4th Edition, Volume 13, page 353), commercially available (cyclo)aliphatic diisocyanates (EP-A 0,289,840) or large-scale production of aromatic diisocyanates (DE-OS 4,217,019 or EP-A-0593334).
(Cyclo)aliphatic 1,2- and 1,3-diisocyanates are frequently mentioned in the literature. However, these diisocyanates are not available in commercial quantities. These diisocyanates can not be produced by the classical phosgenation of the corresponding diamines in the liquid phase in high enough yields to justify their commercial production. In addition to the low yields of the raw product, the high loss of product during the working-up process (in some cases, only 30% of the isocyanate formed originally is recovered) has discouraged commercial production of these diisocyanates.
Conventional phosgenation of 1,3-diaminopentane in the liquid phase results in raw product yields of about 30% and yields of isolated product of about 10%. (E.I. DuPont and Co., Res. Discl., 335, 195 dated 1992 and work by the writer). Other disadvantages of the conventional liquid phase phosgenation process are the lengthy hot phosgenation times and the large excesses of phosgene required.
Phosgenation of 2,4(6)-diamino-1-methylcyclohexane in the liquid phase generally produces unsatisfactory yields of the corresponding diisocyanate. However, yields of up to 89% and of 92% are disclosed in German Offenlegungsschrift 2,005,309 and in Belgian Patent 745,440. These yields are reduced, however, during working-up of the raw products.